CRC_mem

Description

This function calculates the CRC of individual bytes one at a time.

Before the CRC library is included, the constant CRC_POLY must be defined. Valid values are:

	const CRC_POLY = 0x1021		// CRC CCITT
	const CRC_POLY = 0x8408		// CRC CCITT reversed
	const CRC_POLY = 0x8005		// CRC16
	const CRC_POLY = 0xA001		// CRC16 reversed

Before a CRC calculation is started, the CRC accumulator must be initialised to either all zeros or all ones. Using all ones gives better error detection for some zero bit sequences but since it is common practice to use all zeros as the inital value then it is recommended that all zeros be used.

e.g.

	const CRC_POLY = 0x1021		// CRC CCITT
	include "crc_lib.bas"

	uint	acc
	ubyte	arr[10]

	// init CRC acc
	acc = 0

	for j=0 while j<10 step j+=1 do
		acc = CRC_byte(acc, arr[j])
	done

	// CRC for arr is not in acc

Definition

uint CRC_byte(uint acc, ubyte data)

Library

LIB/crc_lib.bas

Usage

On entry:

acc is the CRC accumulator, the CRC is calulated in this variable
data is the byte to be included in the CRC calculation

On exit:

return 16 bit CRC